Perpendicular magnetic recording medium and magnetic storage apparatus

ABSTRACT

A perpendicular magnetic recording medium includes a nonmagnetic seed layer, a nonmagnetic intermediate layer provided on the nonmagnetic seed layer, and a perpendicular recording layer provided on the nonmagnetic intermediate layer. The nonmagnetic seed layer includes a first seed layer made of a Ni alloy having a fcc structure, and a second seed layer provided between the first seed layer and the nonmagnetic intermediate layer and made of a Ni alloy having a fcc structure. A content of one or more elements other than Ni within the Ni alloy forming the second seed layer and having a Goldschmidt radius greater than that of Ni is larger than a content of one or more elements other than Ni within the Ni alloy forming the first seed layer and having a Goldschmidt radius greater than that of Ni.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2008-142917, filed on May 30,2008, the entire contents of which are incorporated herein by reference.

FIELD

The present invention generally relates to magnetic recording media andmagnetic storage apparatuses, and more particularly to a perpendicularmagnetic recording medium which employs the perpendicular magneticrecording technique and a magnetic storage apparatus having such aperpendicular magnetic recording medium.

BACKGROUND

Magnetic storage apparatuses typified by magnetic disk drives include abuilt-in type which is built into a personal computer (PC) or the like,and an external type which is connected externally to the PC or thelike. In such magnetic storage apparatuses, there are demands toincrease the surface recording density of the magnetic recording mediumin order to increase the storage capacity of the magnetic storageapparatus.

Recently, magnetic storage apparatuses employing the perpendicularmagnetic recording technique, having a high recording bit stability evenat high recording densities, have been reduced to practice. Whenincreasing the surface recording density of the magnetic recordingmedium, it is necessary to reduce the medium noise in the perpendicularmagnetic recording medium which employs the perpendicular magneticrecording technique, similarly as in the case of the magnetic recordingmedium employing the horizontal (or in-plane) magnetic recordingtechnique.

A proposal has been made to use a granular magnetic layer for aperpendicular recording layer of the perpendicular magnetic recordingmedium in order to reduce the medium noise. In the granular magneticlayer, a nonmagnetic material, such as an oxide or a nitride, is formedat a grain boundary of magnetic grains to magnetically separate orisolate the magnetic grains, in order to reduce the medium noise. Inaddition, various methods have been proposed to promote the magneticseparation or isolation of the magnetic grains in the granular magneticlayer. For example, a Japanese Laid-Open Patent Publication No.2005-353256 proposes a method of separating crystal grains of anonmagnetic intermediate layer immediately under the perpendicularrecording layer by a gap.

In order to further increase the surface recording density of theperpendicular magnetic recording medium, it is necessary to furtherimprove the signal-to-noise ratio (SNR). Presently, the mainstreammeasures for further improving the SNR reduces the medium noise. Inorder to reduce the medium noise, it is necessary to reduce the magneticgrain size, make the magnetic grain size uniform, and reduce the crystalorientation dispersion of the perpendicular recording layer. In thisspecification, the reducing of the crystal orientation dispersion of thecrystal grains such as the magnetic grains will be referred to asachieving high (or improved) orientation. The nonmagnetic intermediatelayer provided immediately under the perpendicular recording layer playsan important role in determining the magnetic grain characteristicsdescribed above. If the reduction of the grain size, reduction of thecrystal orientation dispersion and the high orientation can be achievedwith respect to the crystal grains of the nonmagnetic intermediatelayer, it would be possible to reduce the grain size, reduce the crystalorientation dispersion and achieve the high orientation with respect tothe perpendicular recording layer that is epitaxially grown on thenonmagnetic intermediate layer.

A technique has been proposed to provide a seed layer immediately underthe nonmagnetic intermediate layer in order to reduce the grain size,reduce the crystal orientation dispersion and achieve the highorientation with respect to the nonmagnetic intermediate layer. Forexample, a Japanese Laid-Open Patent Publication No. 2007-179598proposes providing a NiW seed layer having a face centered cubic (fcc)structure immediately under a Ru intermediate layer having a hexagonalclose packed (hcp) structure. However, according to the medium structureproposed in the Japanese Laid-Open Patent Publication No. 2007-179598,reducing the crystal grain size of the seed layer and achieving the highorientation of the crystal grains of the seed layer are in a tradeoffrelationship, and there was a limit to simultaneously reducing thecrystal grain size and achieving the high orientation of the seed layer.For this reason, there was a limit to simultaneously reducing thecrystal grain size of the perpendicular recording layer and achievingthe high orientation of the perpendicular recording layer. Consequently,there was a limit to further reducing the medium noise in theconventional perpendicular magnetic recording medium, and there was alimit to further increasing the surface recording density of theconventional perpendicular magnetic recording medium.

The applicants are also aware of Japanese Laid-Open Patent PublicationsNo. 2001-155321, No. 2007-257804 and No. 2007-184019. The applicants arefurther aware of Toshio Ando et al., “Tripple-Layer PerpendicularRecording Media for High SN Ratio and Signal Stability”, IEEETransactions on Magnetics, Vol. 33, No. 5, September 1997, pp.2983-2985, and S. S. P. Parkin, “Systematic Variation of the Strengthand Oscillation Period of Indirect Magnetic Exchange Coupling throughthe 3d, 4d, and 5d Transition Metals”, Physical Review Letters, Vol. 67,No. 25, Dec. 16, 1991, pp. 3598-3601.

Therefore, in the conventional perpendicular magnetic recording media,there were problems in that there is a limit to simultaneously reducingthe magnetic grain size and achieving the high orientation of theperpendicular recording layer, and that it is difficult to furtherreduce the medium noise.

SUMMARY

Accordingly, it is an object in one aspect of the invention to provide aperpendicular magnetic recording medium and a magnetic storageapparatus, which can simultaneously reduce the magnetic grain size andachieve the high orientation of the perpendicular recording layer, andfurther reduce the medium noise.

One aspect of the present invention is to provide a perpendicularmagnetic recording medium including a nonmagnetic seed layer, anonmagnetic intermediate layer provided on the nonmagnetic seed layer,and a perpendicular recording layer provided on the nonmagneticintermediate layer, wherein the nonmagnetic seed layer includes a firstseed layer made of a Ni alloy having a fcc structure, and a second seedlayer provided between the first seed layer and the nonmagneticintermediate layer and made of a Ni alloy having a fcc structure, and acontent of one or more elements other than Ni within the Ni alloyforming the second seed layer and having a Goldschmidt radius greaterthan that of Ni is larger than a content of one or more elements otherthan Ni within the Ni alloy forming the first seed layer and having aGoldschmidt radius greater than that of Ni.

Another aspect of the present invention is to provide a magnetic storageapparatus including at least one magnetic recording medium, and atranducer configured to write information on the magnetic recordingmedium and/or read information from the magnetic recording medium,wherein the magnetic recording medium employs a perpendicular magneticrecording technique and has a structure described above.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view illustrating a portion of aperpendicular magnetic recording medium in an embodiment of the presentinvention;

FIG. 2 is a diagram illustrating characteristics of embodiment samplesand comparison samples;

FIG. 3 is a cross sectional view illustrating a portion of a magneticstorage apparatus in an embodiment of the present invention; and

FIG. 4 is a plan view illustrating a portion of the magnetic storageapparatus illustrated in FIG. 3 in a state with a top cover removed.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention will be described withreference to the accompanying drawings.

According to one aspect of the present invention, a perpendicularmagnetic recording medium has a structure in which a nonmagneticintermediate layer is provided between a nonmagnetic seed layer and aperpendicular recording layer. In addition, the nonmagnetic seed layerincludes a first seed layer made of a Ni alloy having a fcc structure,and a second seed layer provided between the first seed layer and thenonmagnetic intermediate layer and made of a Ni alloy having a fccstructure. A content of one or more elements other than Ni within the Nialloy forming the second seed layer and having a Goldschmidt radiusgreater than that of Ni is larger than a content of one or more elementsother than Ni within the Ni alloy forming the first seed layer andhaving a Goldschmidt radius greater than that of Ni.

The present inventors have found that, when the nonmagnetic seed layeris formed by the first seed layer made of the Ni alloy having the fccstructure and the second seed layer made of the Ni alloy having the fccstructure, and the content of one or more elements other than Ni withinthe Ni alloy forming the second seed layer and having a Goldschmidtradius greater than that of Ni is larger than the content of one or moreelements other than Ni within the Ni alloy forming the first seed layerand having a Goldschmidt radius greater than that of Ni, it is possibleto simultaneously reduce the crystal grain size of the nonmagnetic seedlayer and achieve high orientation of the nonmagnetic seed layer.

By simultaneously reducing the crystal grain size and achieving the highorientation of the seed layer, it becomes possible to simultaneouslyreduce the magnetic grain size of the perpendicular recording layer andachieve high orientation of the perpendicular recording layer. For thisreason, it becomes possible to reduce the medium noise, and to furtherincrease the surface recording density.

In other words, in a perpendicular magnetic recording medium and amagnetic storage apparatus according to one aspect of the presentinvention, it is possible to simultaneously reduce the magnetic grainsize and achieve the high orientation of the perpendicular recordinglayer, and further reduce the medium noise.

FIG. 1 is a cross sectional view illustrating a portion of aperpendicular magnetic recording medium in an embodiment of the presentinvention. For example, a perpendicular magnetic recording medium 10illustrated in FIG. 1 is a magnetic disk.

The perpendicular recording medium 10 has a structure including a softmagnetic underlayer 12, a nonmagnetic seed layer 13, a nonmagneticintermediate layer 14, a perpendicular recording layer and a protectionlayer 16 which are successively stacked on a nonmagnetic substrate 11.In order to improve the adhesion or to control the magnetic anisotropyof the soft magnetic underlayer 12, a seed layer (not illustrated) mayfurther be provided between the nonmagnetic substrate 11 and the softmagnetic underlayer 12. A lubricant layer 17 is provided on theprotection layer 16.

In this embodiment, the nonmagnetic substrate 11 is formed by a glasssubstrate. However, the nonmagnetic substrate 11 is not limited to theglass substrate, and other substrates such as a chemically strengthenedglass substrate, a crystalline glass substrate, a NiP-plated Alsubstrate, a NiP-plated Al alloy substrate, a plastic substrate, a Sisubstrate, and a thermally oxidized Si substrate may be used for thenonmagnetic substrate 11.

The soft magnetic underlayer 12 may have a stacked structure made up oftwo or more layers, in order to control the magnetic domains of the softmagnetic underlayer 12 itself, for example. In this embodiment, the softmagnetic underlayer 12 has a stacked structure including a soft magneticlayer 12-1, a nonmagnetic separation layer 12-2 and a soft magneticlayer 12-3.

The soft magnetic layer 12-1 is made of FeCoTaZr, for example. However,the soft magnetic layer 12-1 may be made of other soft magneticmaterials in the amorphous or microcrystalline structure region, such asCoZrNb, CoNbTa, FeCoZrNb, FeCoB, FeCoCrB, NiFeSiB, FeAlSi, FeTaC, FeHfCand NiFe. It is desirable that the soft magnetic material has theamorphous or microcrystalline structure in order to reduce the noisefrom the nonmagnetic underlayer 12. The nonmagnetic separation layer12-2 is made of Ru, for example. However, the nonmagnetic separationlayer 12-2 may be made of materials other than Ru, such as the materialsdisclosed in S. S. P. Parkin, “Systematic Variation of the Strength andOscillation Period of Indirect Magnetic Exchange Coupling through the3d, 4d, and 5d Transition Metals”, Physical Review Letters, Vol. 67, No.25, Dec. 16, 1991, pp. 3598-3601. The soft magnetic layer 12-3 is madeof FeCoNbZr, for example.

The soft magnetic underlayer 12 may be omitted. However, it is desirableto provide the soft magnetic underlayer 12 in order to obtain arecording magnetic field and a magnetic field gradient that are large.

The nonmagnetic seed layer 13 includes a first seed layer 13-1 made of aNi alloy having a fcc structure, and a second seed layer 13-2 made of aNi alloy having a fcc structure. A content of one or more elements otherthan Ni within the Ni alloy forming the second seed layer and having aGoldschmidt radius greater than that of Ni is larger than a content ofone or more elements other than Ni within the Ni alloy forming the firstseed layer and having a Goldschmidt radius greater than that of Ni. TheGoldschmidt radius refers to a radius of a rigid sphere when the crystalstructure of a single element is reproduced as a rigid sphere model,that is, the atomic radius.

In the soluble range of the Ni alloy, the larger the ratio of theelements having a Goldschmidt radius greater than that of Ni which isthe main component, the smaller the crystal grain size tends to be.However, at the same time, the crystal orientation dispersion increases.For this reason, it was difficult to simultaneously reduce the crystalgrain size and achieve the high orientation by adjusting the compositionof the seed layer. In this embodiment, the effect of reducing thecrystal grain size required of the first seed layer 13-1 is not verylarge, but the effect of improving the high orientation of the crystalgrains required of the first seed layer 13-1 is important. On the otherhand, what is required of the second seed layer 13-2 is the effect ofreducing the crystal grain size in order to promote reduction of thecrystal grain size of the nonmagnetic intermediate layer 14 providedimmediately above the second seed layer 13-2. By providing the first andsecond seed layers 13-1 and 13-2 which generate the effects requiredthereby, it is possible to simultaneously reduce the crystal grain sizeand achieve the high orientation.

The first seed layer 13-1 is preferably made of a Ni alloy having thefcc structure and including Ni as a main component and at least oneelement selected from a group consisting of W, Nb, Ta, Mo and Zr. On theother hand, the second seed layer 13-2 is preferably made of a Ni alloyhaving the fcc structure and including Ni as a main component and atleast one element selected from a group consisting of W, Nb, Ta, Mo, Zrand Al. W, Nb, Ta, Mo, Zr and Al have Goldschmidt radii greater thanthat of Ni, and easily become an origin of crystal defect when added toNi. When the crystal defect is generated, the crystal grain boundariesare induced and the crystal grain diameter of the Ni alloy is moreeasily reduced. Furthermore, the solubility limit of W, Nb, Ta, Mo, Zrand Al with respect to Ni is 10 at. % and relatively high, and thecrystal grain size can be reduced while maintaining the crystalstructure of the Ni alloy. The crystal grain size can be reduced byincreasing the amount of the additive element that has the Goldschmidtradius greater than that of Ni and is added to Ni, however, the crystalorientation deteriorates with the increasing amount of the additiveelement. In this embodiment, a composition ratio of all elements otherthan Ni within the Ni alloy is limited to 16 at. % or less, because thelattices are not formed and the Ni alloy becomes amorphous if thecomposition ratio of all elements other than Ni within the Ni alloyexceeds 16 at. %. Hence, the composition ratios of the first and secondseed layers 13-1 and 13-2 are selected so that the crystal grain size ofthe first seed layer 13-1 becomes larger than the crystal grain size ofthe second seed layer 13-2.

In this embodiment, both the first and second seed layers 13-1 and 13-2need to have the crystal structure. The Ni alloy forming the first andsecond seed layers 13-1 and 13-2 needs to form the crystals withrelative ease and have a composition in the soluble range with respectto the composition ratio of all elements (that is, additive elements)other than Ni within the Ni alloy. Accordingly, as will be describedlater in conjunction with FIG. 2, the range of the composition ratio ofall elements other than Ni is selected for each of the first and secondseed layers 13-1 and 13-2, depending on an upper limit and a lower limitof the range in which satisfactory characteristics of the perpendicularmagnetic recording medium 10 are obtained. The composition ratio of allelements other than Ni for the first seed layer 13-1 is 1 at. % to 12at. %. On the other hand, the composition ratio of all elements otherthan Ni for the second seed layer 13-2 is 2 at. % to 16 at. %.

In general, large crystal grains are unlikely formed in an alloy whichis made up of elements having different Goldschmidt radii. This holdstrue for 2-element alloys and 3-element alloys, for example.Accordingly, even if a 2-element alloy Ni—X (where X denotes anarbitrary additive element) is used for the second seed layer 13-2, thelayer structure of the second seed layer 13-2, including the crystalstructure, the crystal grain size and the crystal orientation, becomessimilar as long as the additive element X has a composition ratio in anappropriate range. However, depending on the additive element, thesecond seed layer 13-2 may not become nonmagnetic because Ni which formsthe parent phase is a magnetic material. Because it is desirable to formthe crystalline seed layer from a nonmagnetic material, this embodimentuses as the additive element an element which makes the crystalline seedlayer nonmagnetic even if only a small amount is added to Ni. Hence, thefirst seed layer 13-1 is made of a Ni alloy having the fcc structure andincluding Ni as the main component and at least one element selectedfrom a group consisting of W, Nb, Ta, Mo and Zr, where the compositionratio of all elements other than Ni within the Ni alloy forming thefirst seed layer is 1 at. % to 12 at. %. On the other hand, the secondseed layer 13-2 is made of a Ni alloy having the fcc structure andincluding Ni as the main component and at least one element selectedfrom a group consisting of W, Nb, Ta, Mo, Zr and Al, where thecomposition ratio of all elements other than Ni within the Ni alloyforming the second seed layer is 2 at. % to 16 at. %.

Although it depends on the material forming the layer providedimmediately under the first seed layer 13-1, in general, an extremelythin film having a film thickness of 1 nm or less is unlikely to form acontinuous layer structure in an in-plane direction of the thin film andan island-like discontinuous layer structure is more likely formedinstead. If the first seed layer 13-1 has such a discontinuous layerstructure, the crystal grain size of the second seed layer 13-1 providedimmediately above the first seed layer 13-1 may be reduced and thecrystal grain size distribution of the second seed layer 13-2 may becomeuniform, however, the crystal orientation of the second seed layer 13-2will deteriorate and it will be impossible to achieve a highorientation.

In addition, if the film thickness of the first seed layer 13-1 exceeds5 nm, a crystal structure unique to the material begins to appear, and ahigh orientation of the crystal grains is unlikely to be achieved. Inaddition, if the film thickness of the first seed layer 13-1 exceeds 5nm, a distance between a head (not illustrated) and the soft magneticunderlayer 12 increases. The distance between the head and the softmagnetic underlayer 12 affects the recording characteristic such as therecording magnetic field intensity and the recording magnetic fieldgradient. In order to generate a sufficiently large and sharp recordingmagnetic field for the high-density recording, the distance between thehead and the soft magnetic underlayer 12 needs to be short. For thisreason, the film thickness of the first seed layer 13-1 in thisembodiment may be set in a range which enables the fcc structure, but ispreferably set to 1 nm to 5 nm, and more preferably to 2 nm to 4 nm.

From the point of view of reducing the crystal grain size, the filmthickness of the second seed layer 13-2 is desirably set in a relativelythin range such that the crystal grain size will not become large. Onthe other hand, from the point of view of crystal orientation, the filmthickness of the second seed layer 13-2 is desirably set in a relativelythick range such that the crystallinity is obtained to as certainextent. Moreover, from the point of view of the recording characteristicby taking into consideration the distance between the head and the softmagnetic underlayer 12, the film thickness of the second seed layer 13-2is desirably set in a relatively thin range. For this reason, the filmthickness of the second seed layer 13-2 in this embodiment may be set ina range which enables the fcc structure, but is preferably set to 1 nmto 5 nm, and more preferably to 2 nm to 4 nm.

When the film thickness of the nonmagnetic seed layer 13 as a wholeincreases, it takes more time to perform the production process, and therecording characteristic deteriorate because the distance between thehead and the soft magnetic underlayer 12 increases. Accordingly, thefilm thickness of the nonmagnetic seed layer 13 as a whole is preferablyset to 10 nm or less, and more preferably to 8 nm or less. Furthermore,in order to obtain satisfactory crystal structures for the first andsecond seed layers 13-1 and 13-2, the film thickness of the nonmagneticseed layer 13 as a whole is preferably set to 2 nm or greater, and morepreferably to 3 nm or greater.

The nonmagnetic intermediate layer 14 has a stacked structure which ismade up of one or more layers and includes, at an uppermost surfaceportion thereof, at least a nonmagnetic intermediate layer made of Ru oran Ru alloy including Ru as a main component such that Ru is 50 at. % ormore. The Ru or Ru alloy has a columnar structure in which the crystalgrains are mutually separated by gaps. For example, the structuredisclosed in the Japanese Laid-Open Patent Publication No. 2005-353256may be used for the structure of the nonmagnetic intermediate layer 14.In this embodiment, the nonmagnetic intermediate layer 14 includes a Runonmagnetic intermediate layer 14-1 and a Ru nonmagnetic intermediatelayer 14-2. The Ru nonmagnetic intermediate layer 14-2 has a structurein which the crystal grains are physically separated by the gaps. Ofcourse, the nonmagnetic intermediate layer 14 is not limited to such a2-layer structure, and may be formed by any structure at least having anonmagnetic layer such as the nonmagnetic intermediate layer 14-2 withthe structure in which the crystal grains are physically separated bythe gaps, at the uppermost surface portion of the nonmagneticintermediate layer 14.

The perpendicular recording layer 15 includes at least a granularmagnetic layer having a columnar structure in which the magnetic grainsare isolated in the non-soluble phase. In order to improve the recordingand reproducing characteristics, the perpendicular recording layer 15may have a multi-layer structure made up of two or more granularmagnetic layers. In addition, in the case where the perpendicularrecording layer 15 has the multi-layer structure made up of two or moregranular magnetic layers, a nonmagnetic layer or a slightly magneticlayer may be provided between the granular magnetic layers. Furthermore,in order to improve the recording characteristic and the corrosionresistance, a magnetic layer having the so-called continuous layerstructure may be provided on the granular magnetic layer. In thisembodiment, the perpendicular recording layer 15 includes a granularmagnetic layer (first magnetic layer) 15-1, and a continuous magneticlayer (second magnetic layer) 15-2 which functions as a write-assistlayer having the continuous layer structure. For example, the granularmagnetic layer 15-1 is made of a CoCrPt alloy, and the continuousmagnetic layer 15-2 is made of a CoCrPtB alloy. In this case, thegranular magnetic layer 15-1 has a columnar structure in which theCoCrPt alloy grains are isolated in the non-soluble phase. The magneticanisotropy of the continuous magnetic layer 15-2 is smaller than that ofthe granular magnetic layer 15-1.

For example, the protection layer 16 is made of diamond-like carbon(DLC), and has a film thickness of 4.0 nm. For example, the lubricantlayer 17 is made of a fluorine lubricant, and has a film thickness of1.0 nm.

Next, a description will be given of a method of producing theperpendicular magnetic recording medium 10. Embodiment samples Emb1through Emb13 of this embodiment and comparison samples Cmp1 throughCmp5 of comparison examples were made in the following manner.

Embodiment Sample Emb1

A NiP-plated Al alloy substrate was used for the nonmagnetic substrate11 of the embodiment sample Emb1.

The magnetic domains of the soft magnetic underlayer 12 is desirablycontrolled in order to suppress leakage magnetic flux from the softmagnetic underlayer 12. The techniques that may be used to control themagnetic domains of the soft magnetic underlayer 12 includes the methodof aligning the magnetization directions of the nonmagnetic underlayeras proposed in Toshio Ando et al., “Tripple-Layer PerpendicularRecording Media for High SN Ratio and Signal Stability”, IEEETransactions on Magnetics, Vol. 33, No. 5, September 1997, pp. 2983-2985or, the method of antiferro-magnetically coupling soft magneticunderlayers separated by an extremely thin nonmagnetic separation layeras proposed in the Japanese Laid-Open Patent Publication No.2001-155321. In this embodiment, the soft magnetic layer 12-1, thenonmagnetic separation layer 12-2 and the soft magnetic layer 12-3 werestacked on the nonmagnetic substrate 11 as illustrated in FIG. 1,similarly to the latter proposed method.

The lower soft magnetic layer 12-1 was formed by depositing FeCoTaZr toa film thickness of 25 nm by direct current (DC) sputtering at 0.5 Paand a power of 1 kW in an Ar atmosphere. The film thickness of thenonmagnetic underlayer 12 as a whole is preferably 10 nm or greater fromthe point of view of the recording and reproducing characteristics whena saturation magnetic flux density Bs of the nonmagnetic underlayer 12is 1 (T) or higher, and is more preferably 30 nm or greater. Inaddition, from the point of view of the mass production facility and thecost, the film thickness of the nonmagnetic underlayer 12 as a whole ispreferably 100 nm or less, and more preferably 60 nm or less.

In the following description, it is assumed that the DC sputtering isused for the deposition unless specifically indicated. However, thedeposition method of each layer is of course not limited to the DCsputtering, and other suitable methods may be employed, such as radiofrequency (RF) sputtering, pulse DC sputtering, and CVD.

Next, the nonmagnetic separation layer 12-2 was formed on the FeCoNbZrsoft magnetic layer 12-1 by depositing Ru to a film thickness of 0.4 nmat 0.5 Pa and a power of 150 W in an Ar atmosphere. The film thicknessof the Ru nonmagnetic separation layer 12-2 was selected so that themagnetizations of the adjacent magnetic layers becomeantiferro-magnetically coupled. When Ru is used for the nonmagneticseparation layer 12-2, the film thickness in general is selected to asuitable value on the order of 0.5 nm to 1 nm.

Next, the soft magnetic layer 12-3 was formed on the Ru nonmagneticseparation layer 12-2 by depositing FeCoNbZr to a film thickness of 25nm by DC sputtering at 0.5 Pa and a power of 1 kW in an Ar atmosphere.

The nonmagnetic seed layer 13 was deposited on the nonmagneticunderlayer 12. The nonmagnetic seed layer 13 was formed from a firstseed layer 13-1 having a fcc structure and a second seed layer 13-2having a fcc structure. When NiW was used for the first seed layer 13-1and NiWNb was used for the second seed layer 13-2, it was confirmed thatthe crystal grain size can be reduced and the high orientation can beachieved simultaneously. In the embodiment sample Emb1, the first seedlayer 13-1 was formed by depositing Ni₉₂W₈ to a film thickness of 3.2 nmby DC sputtering at 0.5 Pa and a power of 150 W in an Ar atmosphere. Inaddition, the second seed layer 13-2 was formed by depositing Ni₈₆W₈Nb₆to a film thickness of 3.2 nm by DC sputtering at 0.5 Pa and a power of100 W in an Ar atmosphere.

The film thickness of the first seed layer 13-1 may be set within anyrange which will enable the fcc structure to be obtained. However, ifthe first seed layer 13-1 is too thin, the first seed layer 13-1 itselfwill not become a continuous layer and cause deterioration of thecrystal orientation of the nonmagnetic intermediate layer 14 and thelayers provided above the nonmagnetic intermediate layer 14. On theother hand, if the first seed layer 13-1 is too thick, the distancebetween the head and the soft magnetic underlayer 12 will become longand cause undesirable effects of the recording characteristic.Accordingly, it was confirmed that the film thickness of the first seedlayer 13-1 is preferably set to 1 nm to 5 nm, and more preferably to 2nm to 4 nm.

The film thickness of the second seed layer 13-2 may be set within anyrange which will enable the fcc structure to be obtained. The secondseed layer 13-2 should be set in a thin range from the point of view ofreducing the grain size so that the crystal grain size will not becomelarge, but the second seed layer 13-2 should have crystallinity to acertain extent from the point of view of the crystal orientation. Inaddition, the second seed layer 13-2 should be thin from the point ofview of the recording characteristic. Accordingly, it was confirmed thatthe film thickness of the second seed layer 13-2 is preferably set to 1nm to 5 nm, and more preferably to 2 nm to 4 nm.

The nonmagnetic intermediate layer 14 was deposited on the nonmagneticseed layer 13. In the embodiment sample Emb1, the following stackedstructure was employed in order to promote the magnetic isolation of themagnetic crystals in the granular magnetic layer 15-1. That is, thenonmagnetic intermediate layer 14-1 was formed by depositing Ru to afilm thickness of 14 nm at 0.67 Pa and a power of 800 W in an Aratmosphere. Then, the nonmagnetic intermediate layer 14-2 was formed bydepositing Ru to a film thickness of 7 nm by at 5 Pa and a power of 300W in an Ar atmosphere. The nonmagnetic intermediate layer 14-2 has thestructure in which the crystal grains are physically separated by thegaps due to the effects of the high-pressure gas and the low depositionrate.

Next, the perpendicular recording layer 15 was deposited on thenonmagnetic intermediate layer 14. In the embodiment sample Emb1, thestructure disclosed in the Japanese Laid-Open Patent Publication No.2007-257804, for example, was used for the perpendicular recording layer15 in order to obtain satisfactory recording and reproducingcharacteristics. In other words, the continuous magnetic layer 15-2having the so-called continuous layer structure was provided on thegranular magnetic layer 15-1 which is provided closer to the nonmagneticsubstrate 11 than the continuous magnetic layer 15-2. First, thegranular magnetic layer 15-1 was formed by depositing92(66Co-13Cr-21Pt)-8TiO2 to a film thickness of 8 nm at 4 Pa and a powerof 300 W in an Ar atmosphere. Then, the continuous magnetic layer 15-2was formed on the granular magnetic layer 15-1 by depositing63Co-20Cr-13Pt-4B to a film thickness of 7 nm at 0.5 Pa and a power of400 W in an Ar atmosphere.

The DLC protection layer 16 was deposited on the perpendicular recordinglayer 15 to a film thickness of 4 nm by CVD. In addition, the lubricantlayer 17 was formed on the protection layer 16 to a film thickness of 1nm by coating a fluorine lubricant on the protection layer 16 andremoving projections and foreign particles on the coated surface by useof a polishing tape.

Embodiment Sample Emb2

The total film thickness of the first seed layer 13-1 and the secondseed layer 13-2 was set constant to 6.4 nm, and the film thickness ofeach of the first and second seed layers 13-1 and 13-2 was varied forthe embodiment sample Emb2, under the same conditions used for theembodiment sample Emb1, in order to study the dependence of thecharacteristics of the perpendicular magnetic recording medium 10 on thefilm thickness of the first seed layer 13-1. The total film thickness ofthe first and second seed layers 13-1 and 13-2 was maintained constantso that the recording capability of the head will be the same when latercomparing the recording and reproducing characteristics of the samples.

In the embodiment sample Emb2, the first seed layer 13-1 was formed by a5.0 nm thick Ni₉₂W₈, and the second seed layer 13-2 was formed by a 1.4nm thick Ni₈₆W₈Nb₆.

Embodiment Sample Emb3

The embodiment sample Emb3 was made under the same conditions as theembodiment sample Emb1, except that the first seed layer 13-1 was formedby a 1.5 nm thick Ni₉₂W₈, and the second seed layer 13-2 was formed by a4.9 nm thick Ni₈₆W₈Nb₆.

Comparison Sample Cmp1

The comparison sample Cmp1 of the comparison example was made under thesame conditions as the embodiment sample Emb1, except that no secondseed layer 13-2 was formed and the thickness of the first seed layer13-2 was 0, and the first seed layer 13-1 was formed by a 6.4 nm thickNi₉₂W₈.

Comparison Sample Cmp2

The comparison sample Cmp2 of the comparison example was made under thesame conditions as the embodiment sample Emb1, except that no first seedlayer 13-1 was formed and the thickness of the first seed layer 13-1 was0, and the second seed layer 13-2 was formed by a 6.4 nm thickNi₈₆W₈Nb₆.

Embodiment Sample Emb4

The embodiment sample Emb4 was made under the same conditions as theembodiment sample Emb1, except that the first seed layer 13-1 was formedby a 5.0 nm thick Ni₉₂W₈, and the second seed layer 13-2 was formed by a1.4 nm thick Ni₈₆W₈Al₆.

Embodiment Sample Emb5

The embodiment sample Emb5 was made under the same conditions as theembodiment sample Emb4, except that the first seed layer 13-1 was formedby a 3.2 nm thick Ni₉₂W₈, and the second seed layer 13-2 was formed by a3.2 nm thick Ni₈₆W₈Al₆.

Embodiment Sample Emb6

The embodiment sample Emb6 was made under the same conditions as theembodiment sample Emb4, except that the first seed layer 13-1 was formedby a 1.5 nm thick Ni₉₂W₈, and the second seed layer 13-2 was formed by a4.9 nm thick Ni₈₆W₈Al₆.

Comparison Sample Cmp3

The comparison sample Cmp3 was made under the same conditions as theembodiment sample Emb4, except that no first seed layer 13-1 was formedand the thickness of the first seed layer 13-1 was 0, and the secondseed layer 13-2 was formed by a 6.4 nm thick Ni₈₆W₈Al₆.

Embodiment Sample Emb7

The embodiment sample Emb7 was made under the same conditions as theembodiment sample Emb1, except that Ni₈₆W₈Ta₆ was used for the secondseed layer 13-2. The first seed layer 13-1 was formed to a thickness of5.0 nm, and the second seed layer 13-2 was formed to a thickness of 1.4nm.

Embodiment Sample Emb8

The embodiment sample Emb8 was made under the same conditions as theembodiment sample Emb7, except that the first seed layer 13-1 was formedby a 3.2 nm thick Ni₉₂W₈, and the second seed layer 13-2 was formed by a3.2 nm thick Ni₈₆W₈Ta₆.

Embodiment Sample Emb9

The embodiment sample Emb9 was made under the same conditions as theembodiment sample Emb7, except that the first seed layer 13-1 was formedby a 1.5 nm thick Ni₉₂W₈, and the second seed layer 13-2 was formed by a4.9 nm thick Ni₈₆W₈Ta₆.

Comparison Sample Cmp4

The comparison sample Cmp4 was made under the same conditions as theembodiment sample Emb7, except that no first seed layer 13-1 was formedand the thickness of the first seed layer 13-1 was 0, and the secondseed layer 13-2 was formed by a 6.4 nm thick Ni₈₆W₈Ta₆.

Comparison Sample Cmp5

The comparison sample Cmp5 was made under the same conditions as theembodiment sample Emb7, except that the first seed layer 13-1 was formedby a 3.2 nm thick Ni₉₂W₈Ta₆, and the second seed layer 13-2 was formedby a 3.2 nm thick Ni₉₂W₈. In other words, the stacking order of thefirst and second seed layers 13-1 and 13-2 in the comparison sample Cmp5is in reverse to the stacking order of the first and second seed layers13-1 and 13-2 in the embodiment sample Emb7.

Embodiment Sample Emb10

The embodiment sample Emb10 was made under the same conditions as theembodiment sample Emb1, except that the total film thickness of thefirst and second seed layers 13-1 and 13-2 was set constant to 6.4 nm,and the composition of the second seed layer 13-2 was changed.

In the embodiment sample Emb10, the first seed layer 13-1 was formed bya 3.2 nm thick Ni₉₂W and the second seed layer 13-2 was formed by a 3.2nm thick Ni₂W Nb₁₀.

Embodiment Sample Emb11

The embodiment sample Emb11 was made under the same conditions as theembodiment sample Emb10, except that the first seed layer 13-1 wasformed by a 3.2 nm thick Ni₉₂W₈, and the second seed layer 13-2 wasformed by a 3.2 nm thick Ni₈₄W₈Nb₈.

Embodiment Sample Emb12

The embodiment sample Emb12 was made under the same conditions as theembodiment sample Emb10, except that the first seed layer 13-1 wasformed by a 3.2 nm thick Ni₉₂W₈, and the second seed layer 13-2 wasformed by a 3.2 nm thick Ni₈₈W₈Nb₄.

Embodiment Sample Emb13

The embodiment sample Emb13 was made under the same conditions as theembodiment sample Emb10, except that the first seed layer 13-1 wasformed by a 3.2 nm thick Ni₉₂W₈, and the second seed layer 13-2 wasformed by a 3.2 nm thick Ni₉₀W₈Nb₂.

FIG. 2 is a diagram illustrating characteristics of embodiment samplesEmb1 through Emb13 and the comparison samples Cmp1 through Cmp5. Thecharacteristics illustrated in FIG. 2 include the grain diameter (nm) ofthe nonmagnetic intermediate layer 14 (the nonmagnetic intermediatelayer 14-1 in the case of this embodiment), the half value width Δθ50(deg) obtained from the rocking curve of the (002) crystal face of Ruforming the nonmagnetic intermediate layer 14, and a SNR (dB) obtainedby performing a test write to and a test read from the perpendicularrecording layer 15 according to a known method. The SNR indicates therecording and reproducing characteristics of the perpendicular magneticrecording medium 10.

The following characteristics were confirmed by comparing the crystalgrain diameters, the half value widths Δθ50 and the SNRs (that is,recording and reproducing characteristics) of the embodiment samplesEmb1 through Emb13 and the comparison samples Cmp1 through Cmp5.

When the comparison samples Cmp1 and Cmp2 were compared with theembodiment samples Emb1 through Emb3 in FIG. 2, it was confirmed thatfor the embodiment samples Emb1 through Emb3, the crystal grain size isreduced and the increase of the crystal orientation dispersion issuppressed simultaneously, and that the SNR improves. On the other hand,when the nonmagnetic seed layer 13 is made up solely of the NiWNb secondseed layer 13-2 as in the case of the comparison sample Cmp2, it wasconfirmed that the crystal grain size can be reduced, but the crystalorientation dispersion increases and the SNR deteriorates. Accordingly,the effect of improving the SNR by the 2-layer structure of thenonmagnetic seed layer 13 formed by the first and second seed layers13-1 and 13-2 was confirmed.

When the comparison samples Cmp1 through Cmp3 and the embodiment samplesEmb4 through Emb9 using different materials for the second seed layer13-2 were compared, it was confirmed that the effect of reducing thecrystal grain size and the effect of suppressing the increase of thecrystal orientation dispersion do not change even if the material usedfor the second seed layer 13-2 is changed. It was also confirmed thatthe extent of the effect of reducing the crystal grain size and theextent of the effect of suppressing the increase of the crystalorientation dispersion changes depending on the material used for thesecond seed layer 13-2. As may be seen from FIG. 2, it was confirmedthat the effect of reducing the crystal grain size and the effect ofsuppressing the increase of the crystal orientation dispersion arelargest for the case where NiWNb is used for the second seed layer 13-2.

In addition, when the comparison sample Cmp5 and the embodiment sampleEmb1 were compared, it was confirmed that if the composition of anelement which is included in the second seed layer 13-2 and is otherthan Ni and has a Goldschmidt radius greater than that of Ni is lessthan or equal to the composition of an element which is included in thefirst seed layer 13-1 and is other than Ni and has a Goldschmidt radiusgreater than that of Ni, the effect of suppressing the crystalorientation dispersion does not appear. It may be regarded that this iscaused by a decrease in the effect of suppressing the crystalorientation dispersion by the first seed layer 13-1.

Furthermore, as may be seen from FIG. 2, it was confirmed that there isan appropriate value or an optimum value for the total amount of theelement which is included in the second seed layer 13-2 and is otherthan Ni and has a Goldschmidt radius greater than that of Ni. In otherwords, the effect of reducing the crystal grain size is small if thetotal amount of the element which is included in the second seed layer13-2 and is other than Ni and has the Goldschmidt radius greater thanthat of Ni is less than or equal to the total amount of the elementwhich is included in the first seed layer 13-1 and is other than Ni andhas a Goldschmidt radius greater than that of Ni. On the other hand, thecrystal orientation dispersion increases if the total amount of theelement which is included in the second seed layer 13-2 and is otherthan Ni and has the Goldschmidt radius greater than that of Ni isexcessively large. For this reason, it was confirmed that the first seedlayer 13-1 is desirably made of an Ni alloy having the fcc structure andincluding Ni as the main component and at least one element selectedfrom a group consisting of W, Nb, Ta, Mo and Zr, that a compositionratio of all elements other than Ni within the Ni alloy forming thefirst seed layer 13-1 is desirably 1 at. % to 12 at. %, and that thefilm thickness of the first seed layer 13-1 is preferably 1 nm to 5 nmand more preferably 2 nm to 4 nm. On the other hand, it was confirmedthat the second seed layer 13-2 is desirably made of an Ni alloy havingthe fcc structure and including Ni as the main component and at leastone element selected from a group consisting of W, Nb, Ta, Mo, Zr andAl, that a composition ratio of all elements other than Ni within the Nialloy forming the second seed layer 13-2 is desirably 2 at. % to 16 at.%, and that the film thickness of the second seed layer 13-2 ispreferably 1 nm to 5 nm and more preferably 2 nm to 4 nm.

According to the embodiment described above, it is possible to form aperpendicular magnetic recording medium which has improved recording andreproducing characteristics over the conventional perpendicular magneticrecording medium. For this reason, it is possible to provide aperpendicular magnetic recording medium having a high recording density,and to provide a magnetic storage apparatus having a large storagecapacity.

Next, a description will be given of the magnetic storage apparatus inone embodiment of the present invention, by referring to FIGS. 3 and 4.FIG. 3 is a cross sectional view illustrating a portion of the magneticstorage apparatus in this embodiment of the present invention, and FIG.4 is a plan view illustrating a portion of the magnetic storageapparatus illustrated in FIG. 3 in a state with a top cover removed.

As illustrated in FIGS. 3 and 4, a motor 114 is mounted on a base 113,and this motor 114 rotates a hub 115 to which a plurality of magneticrecording disks 116 are fixed. Each magnetic recording disk 116 has thestructure of the perpendicular magnetic recording medium 10 illustratedin FIG. 1. Information is read from the magnetic recording disk 116 by amagneto-resistive (MR) heat which is fixed on a slider 117. A giantmagneto-resistive (GMR) heat, a tunneling magneto-resistive (TuMR) heatand the like may be used for the MR head. An inductive head is combinedwith the MR head, and information is written on the magnetic recordingdisk 116 by the inductive head. The MR head and the inductive head forma transducer. The slider 117 is supported on a suspension 118, and thesuspension 118 pushes the slider 117 against a recording surface of themagnetic recording disk 116. The surface of the slider 117 is patterned,and at a specific disk rotational speed and a specific suspensionhardness, the slider 117 scans at a position floating by a predetermineddistance from the recording surface of the magnetic recording disk 116.The suspension 118 is fixed to a rigid arm 119 which is connected to anactuator 120. Accordingly, information can be written over a relativelylarge area on the recording surface of the magnetic recording disk 116.

Of course, the number of magnetic recording disks 116 is not limited tothree as illustrated in FIG. 3. In other words, two or four or moremagnetic recording disks 116 may be provided within the magnetic storageapparatus.

In addition, the perpendicular magnetic recording medium in thisembodiment is not limited to the magnetic recording disk, and thepresent invention is similarly applicable to various types of magneticrecording media including magnetic recording cards, for example.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contribute by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification related to a showing of the superiorityand inferiority of the invention. Although the embodiments of thepresent invention have been described in detail, it should be understoodthat the various changes, substitutions, and alterations could be madehereto without departing from the spirit and scope of the invention.

1. A perpendicular magnetic recording medium comprising: a nonmagneticseed layer; a nonmagnetic intermediate layer provided on the nonmagneticseed layer; and a perpendicular recording layer provided on thenonmagnetic intermediate layer, wherein the nonmagnetic seed layerincludes a first seed layer made of a NiW alloy having a fcc structure,and a second seed layer provided between the first seed layer and thenonmagnetic intermediate layer and made of a NiWNb alloy having a fccstructure, and a content of one or more elements other than Ni withinthe NiWNb alloy forming the second seed layer and having a Goldschmidtradius greater than that of Ni is larger than a content of one or moreelements other than Ni within the NiW alloy forming the first seed layerand having a Goldschmidt radius greater than that of Ni.
 2. Theperpendicular magnetic recording medium as claimed in claim 1, whereinthe first seed layer includes Ni as a main component and W and at leastone element selected from a group consisting of W, Nb, Ta, Mo and Zr. 3.The perpendicular magnetic recording medium as claimed in claim 1,wherein a composition ratio of all elements other than Ni within the NiWalloy forming the first seed layer is 1 at. % to 12 at. %.
 4. Theperpendicular magnetic recording medium as claimed in claim 1, whereinthe first seed layer has a thickness of 1 nm to 5 nm.
 5. Theperpendicular magnetic recording medium as claimed in claim 1, whereinthe first seed layer has a thickness of 2 nm to 4 nm.
 6. Theperpendicular magnetic recording medium as claimed in claim 1, whereinthe second seed layer includes Ni as a main component and W and Nb andat least one element selected from a group consisting of Ta, Mo, Zr andAl.
 7. The perpendicular magnetic recording medium as claimed in claim1, wherein a composition ratio of all elements other than Ni within theNiWNb alloy forming the second seed layer is 2 at. % to 16 at. %.
 8. Theperpendicular magnetic recording medium as claimed in claim 1, whereinthe second seed layer has a thickness of 1 nm to 5 nm.
 9. Theperpendicular magnetic recording medium as claimed in claim 1, whereinthe second seed layer has a thickness of 2 nm to 4 nm.
 10. Theperpendicular magnetic recording medium as claimed in claim 8, wherein atotal thickness of the first and second seed layers is 3 nm or greater.11. The perpendicular magnetic recording medium as claimed in claim 1,wherein the nonmagnetic intermediate layer is made of Ru or an alloyhaving Ru as a main component.
 12. The perpendicular magnetic recordingmedium as claimed in claim 1, further comprising: a substrate; and asoft magnetic underlayer provided on the substrate, wherein the softmagnetic underlayer is made of a crystalline or amorphous materialincluding Co and Fe.
 13. The perpendicular magnetic recording medium asclaimed in claim 1, wherein the perpendicular recording layer includesone or more magnetic layers made of a granular magnetic material. 14.The perpendicular magnetic recording medium as claimed in claim 1,wherein the perpendicular recording layer includes a first magneticlayer made of a granular magnetic material and provided on thenonmagnetic intermediate layer, and a second magnetic layer provided onthe first magnetic layer and having a magnetic anisotropy smaller thanthat of the first magnetic layer.
 15. A magnetic storage apparatuscomprising: at least one magnetic recording medium; and a transducerconfigured to write information on the magnetic recording medium and/orread information from the magnetic recording medium, wherein themagnetic recording medium employs a perpendicular magnetic recordingtechnique and includes a nonmagnetic seed layer, a nonmagneticintermediate layer provided on the nonmagnetic seed layer, and aperpendicular recording layer provided on the nonmagnetic intermediatelayer, wherein the nonmagnetic seed layer includes a first seed layermade of a NiW alloy having a fcc structure, and a second seed layerprovided between the first seed layer and the nonmagnetic intermediatelayer and made of a NiWNb alloy having a fcc structure, and a content ofone or more elements other than Ni within the NiWNb alloy forming thesecond seed layer and having a Goldschmidt radius greater than that ofNi is larger than a content of one or more elements other than Ni withinthe NiW alloy forming the first seed layer and having a Goldschmidtradius greater than that of Ni.
 16. The magnetic storage apparatus asclaimed in claim 15, wherein the first seed layer of the magneticrecording medium includes Ni as a main component and W and at least oneelement selected from a group consisting of W, Nb, Ta, Mo and Zr. 17.The magnetic storage apparatus as claimed in claim 16, wherein the firstseed layer of the magnetic recording medium has a thickness of 1 nm to 5nm.
 18. The magnetic storage apparatus as claimed in claim 15, whereinthe second seed layer includes Ni as a main component and W and Nb andat least one element selected from a group consisting of Ta, Mo, Zr andAl.
 19. The magnetic storage apparatus as claimed in claim 18, whereinthe second seed layer of the magnetic recording medium has a thicknessof 1 nm to 5 nm.
 20. A perpendicular magnetic recording mediumcomprising: a nonmagnetic seed layer; a nonmagnetic intermediate layerprovided on the nonmagnetic seed layer; and a perpendicular recordinglayer provided on the nonmagnetic intermediate layer, wherein thenonmagnetic seed layer includes a first seed layer made of a NiW alloyhaving a fcc structure, and a second seed layer provided between thefirst seed layer and the nonmagnetic intermediate layer and made of aNiW alloy having a fcc structure, and a content of one or more elementsother than Ni within the NiW alloy forming the second seed layer andhaving a Goldschmidt radius greater than that of Ni is larger than acontent of one or more elements other than Ni within the NiW alloyforming the first seed layer and having a Goldschmidt radius greaterthan that of Ni, wherein the first seed layer includes Ni as a maincomponent and W and at least one element selected from a groupconsisting of Nb, Ta, Mo and Zr; and the second seed layer includes Nias a main component and W and at least one element selected from a groupconsisting of Nb, Ta, Mo and Zr.